variable scope in class?

**jonas-e** · Oct 6, 2009 15:26

This is my first attempt ever to build a class in PHP, so please bear with me ..

I don't get any hard errors, but the variable $title doesn't resolve inside the docStart() method; I simply get an emtpy title tag in my html.

Any suggestions how I can access that variable inside the method?

PHP Code:


class Doc {

   

   public $title="TITLE MISSING";

   

   public function setTitle($t) {

      $title=$t;

      return;

   }

   

   public function getTitle() {

      return $title;

   }



   public function docStart() {

      $str= <<<MYSTRING

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">

<html>

<head>

   <title>$title</title>

</head>

<body>

MYSTRING;

      echo $str;

      return;

   }

   

   public function docEnd() {

      echo "\n\n</body></html>";

      return;

   }

}



$myDoc = new Doc;

$myDoc->setTitle("A world of hello!");

$myDoc->docStart();

echo "<h1>HELLO WORLD!</h1>";

$myDoc->docEnd();

**fidel karsto** · Oct 6, 2009 16:09

hi jonas-e,
$title is a so called member property of your Doc class, which means you need to access them inside your class via this: $this->title
In your setter method it should therefore be:

PHP Code:


public function setTitle($t) { 
      $this->title=$t; 
      // return; no return here, setters should return nothing usually 
   }

Accordingly it should be $this->title in your docstart() method.

Because you made the title property public, you can access it outside of your class by using your class instance: $myDoc->title, but for best practice member properties should not be public.
Which means you should set private $title ="..." in your class and access it from outside through a getter method:

PHP Code:


public function getTitle(){
return $this->title;
}

**Salathe** · Oct 6, 2009 18:05

Hi jonas-e,

I'd like to direct you to the portion of the PHP Manual on Classes and Objects (in PHP 5). In there is an extensive overview of everything to do with classes. Of particular note to your problem would be the sections entitled "The Basics" which covers the $this pseudo-variable and "Properties" which covers what properties are all about and how to work with them.

**cranial-bore** · Oct 6, 2009 18:17

The other posts should answer your question, but I just wanted to add it's considered better practice to not echo directly from your class methods. Instead they should return the value and the calling code should echo.

example

PHP Code:


class Doc
{

    // snip....
    
    public function docStart() {
      $str= <<<MYSTRING
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
   <title>$this->title</title>
</head>
<body>
MYSTRING;

      return $str;

   }
}

$myDoc = new Doc;
echo $myDoc->docStart();

**jonas-e** · Oct 7, 2009 00:31

Thanks a lot for your thorough help!

@(fidel karsto): I did intend to make the $title variable private - only tried out the public option to see if it would solve my problem.

I will try calling "$this->title" inside my string next. But how would PHP know that the "->title" is not just another part of the string ..?

@Salathe: Thanks, I shall read the manual.

**fidel karsto** · Oct 7, 2009 01:33

Hi jonas-e,

when your are echoing a string in php with double quotes ("..."), the interpreter will parse variables inside it which are recognized by the $ sign.
In this case the variable "$this" is a self reference to the object instance, which means that "->" will be interpreted as an object accessor to a property or method. If for some reason this should not work out, you should try to concatenate the string like this: "....<title>".$this->title."</title>...."

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